The acrosome reaction must occur for sperm to penetrate the investments surrounding the ovum and ultimately for fertilization to take place. It is believed that the acrosome reaction releases various hydrolytic enzymes needed for the penetration of the ovum. Thus, if these acrosomal enzymes are to avoid dilution in the reproductive tract of the male or female the occurrance of the acrosome reaction must be controlled. This control is likely the result of two factors. First, an acrosome stabilizing factor associated with the sperm at ejaculation. Second, a triggering mechanism which induces the acrosome reaction associated with the products of ovulation. This proposal will focus on the Acrosome Stabilizing Factor (ASF) which has been demonstrated to be produced in the epididymis. The Acrosome Stabilizing Factor from rabbit has been purified to homogenity by this laboratory. In addition thirty different monoclonal antibodies are available fo aid in ASF purification and characterization. This proposal will attempt to: 1) Localize ASF on the sperm collected from the epididymis, at ejaculation, and collected from the female reproductive tract. 2) Utilizing a competitive ELISA assay the amounts of ASF will be determined in the epididymis, during ejaculation, and after mating in the female reproductive tract. 3) Using radiolabeled affinity-purified ASF, interactions of ASF and sperm will be evaluated at the molecular level. 4) Monoclonal antibodies will be used to facilitate defining the domains of ASF associated with sperm binding. Studies of ASF--sperm interactions at the molecular level may yield insights that may lead to new contraception development, new methods for in vitro sperm storage, new methods which may circumvent some unexplained cases of infertility, and new methods to facilitate in vitro fertilization in domestic animals and man.